Acetylene tetramerization

Figure A Cyclic oligomerizations of acetylene tetramerization producing cyclooctatetraene (cot) and trimerization producing benzene.

Cyclooctatetraene can be obtained on an industrial scale by metal carbonyl catalyzed thermal tetramerization of acetylene. If cyclooctatetraene is UV-irradiated at low temperature in the presence of acetone, it is reversibly rearranged to form semibullvalene (H.E. Zimmerman, 1968, 1970). 

Gyclooctatetraene (GOT). Tetramerization of acetylene to cyclooctatetraene [629-20-9], CgHg, although interesting, does not seem to have been used commercially. Nickel salts serve as catalysts. Other catalysts give ben2ene. The mechanism of this cyclotetramerhation has been studied (4). 

Dimerization (E2), Trimerization (E3), and Tetramerization (E4) Energies (in kcal/mol) for Acetylene and LiF Calculated by MNDO and ab Initio Methods... 

At present, HpNC is significantly easier to make than ONC, which is an expensive explosive and also difficult to make. Research is now focused on finding an economical synthetic route and to make it directly by tetramerization of dinitro-acetylene (a compound not yet known). By exploiting the property of TNC (of highly acidic nature) and use of interfacial nitration, TNC is converted to PNC [261]. Acetylene (parent hydrocarbon of dinitroacetylene and a cheap starting material available in abundance) is acidic in nature and therefore, it is speculated that acetylene may be converted to dinitroacetylene by following the approach of conversion of TNC to PNC, followed by its tetramerization resulting in the formation of ONC. 

Scheme 6.25 Alkyne metathesis leads in high yields to the formation of tetrameric carbazole-acetylene macrocycles.

Acetylenes, tri- and tetramerization Bis-(benzonitrile>palladium (II) chloride. Bis-triphenylphosphinecarbonylmckel. Tetrakis-phosphorus trichloride-nickel (0). Titanium tetrachloride. 

Ni or Ti catalyzed tetramerization or trimerization of acetylene and reactions with alcohols, amines, carboxylic acids, thiols (see 1st edition). 

All monomer syntheses begin with cyclooctane, which is obtained either by tetramerization of acetylene to cyclooctatetraene or by dimerization of butadiene to cyclooctadiene, with subsequent hydrogenation to cyclooctane. The cyclooctane is then converted into capryllactam either via the ketone and the oxime or through photoximation with NOCl (cf. nylon 6). Polymerization occurs as for nylon 6. 

When the acetylenic groups are in the para positions on the aromatic ring, condensation with a metal phosphine leads to a linear polymer as in (8.358), but if these groups are in the ortho position a cyclic tetrameric ring is produced as in (8.357) [33]. With three pendant acetylenic groups, dendritic-type structures can be obtained as in (8.356). 

Nickel complexes of alkynes are involved in many important catal)rtic transformations. A fundamental transformation of nickel(0)-alkyne complexes that forms the basis of a number of usefiil stoichiometric and catal)rtic reactions is the oxidative cyclization of one alkyne and a second unsaturated imit to form a five-membered metallacyclopentene 47 (Scheme 29). If the second unsaturated unit is also an aUqme, linear oligomerizations or cydooligomerizations result The catal5rtic tetramerization of acetylene to octatetra-ene was discovered more than 50 years ago by Reppe,l l and an excellent review on the historical development of this area has appeared.Pl The complexities of the mechanistic... 

Through an apparently less complicated process that nonetheless requires com-plexation with an organometallic catalyst, ethyne (acetylene, HC CH) itself undergoes trimerization in the presence of dicobalt octacarbonyl [Co2(CO)g] (Equation 6.69) to benzene and (Equation 6.70) tetramerization in the presence of nickel(II) cyanide [Ni(CN)2] to cyclooctatetraene. 

The self-dimerization of ethyne (acetylene, HOCH) would give rise to the 4n antiaromatic compound cyclobutadiene and, although the metal-catalyzed trimer-ization and tetramerization (vide supra) occur, the reaction (Equation 6.72) is not observed. Interestingly, cyclobutadiene and substituted cyclobutadienes have been prepared by several more circuitous routes and one of the ways of producing cyclobutadiene (albeit temporarily) is shown in Scheme 6.77. 

Diazadiene)2 1 complexes selectively catalyse the cyclo-tetramerization of acetylenes of the type RC = CH and RC = CR (R = CH2OH, CH20Me, CH20-p-tolyl) for disubstituted acetylenes, the reaction proceeds via the intermediacy of the (diazadiene)-Ni(acetylene) complex which can be isolated and structurally characterized where R = CH2OH. For the monosubstituted acetylenes,... 

Phosphenated polystyrene NiCIi PdClit-AgBF4 Cyclotri- and tetramerization of ethyl propiolate and cyclo-trimerization of phenyl-acetylene and various olefins British Petroleum Co. Ltd., 1972 Kaneda et aL, 1977... 

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